Ultraviolet absorbents have been used in combination with various resins for providing the resins with ultraviolet-absorptivity. Both inorganic and organic ultraviolet absorbents are used. The inorganic ultraviolet absorbents (see, for example, JP-A-5-339033 (“JP-A” means unexamined published Japanese patent application), JP-A-5-345639 and JP-A-6-56466) are superior in durability properties such as weather resistance and heat resistance. However, the freedom in selecting the compound is limited, because the absorption wavelength is determined by the band gap of the compound. In addition, there is no inorganic absorbent that absorbs the light in a long-wavelength ultraviolet (UV-A) range of 320 to 400 nm. And any such absorbent that absorbs long-wavelength ultraviolet would have color because it would have absorption also in the visible range.
In contrast, the freedom in designing the absorbent structure is much wider for organic ultraviolet absorbents, and thus, it is possible to obtain absorbents having various absorption wavelengths by designing the absorbent chemical structure properly.
Various organic ultraviolet absorbent systems have been studied, and for absorption in the long-wavelength ultraviolet range, it is conceivable either to use an absorbent having the wavelength of maximal absorption in the long-wavelength ultraviolet range or to use a high concentration of absorbent. However, the absorbents described in, for example, JP-A-6-145387 and JP-A-2003-177235 having the wavelength of maximal absorption in the long-wavelength ultraviolet range are inferior in light stability, and their absorption capacity declines over time.
In contrast, benzophenone- and benzotriazole-based ultraviolet absorbents are relatively superior in light stability, and increase in concentration or film thickness leads to relatively clean blocking of the light in the longer-wavelength range (see, for example, JP-T-2005-517787 (“JP-T” means published Japanese translation of PCT application) and JP-A-7-285927). However, when such an ultraviolet absorbent is applied as mixed with a resin or the like, the film thickness is limited to several tens of μm at the most. For utilizing the film thickness to block the light in the longer-wavelength range, it is necessary to add the ultraviolet absorbent to a considerably high concentration. In such a case, there were problems of precipitation of the ultraviolet absorbent and bleed-out during long-term use. In addition, among benzophenone-based and benzotriazole-based ultraviolet absorbents, there are some ultraviolet absorbents that may cause concern about skin irritation and accumulation in body. JP-A-2007-304287, JP-A-60-170842 and JP-B-49-11155 (“JP-B” means examined Japanese patent publication) describe a five-membered ring compound containing two sulfur atoms.